LIGHTWEIGHT, laid-back and mechanically straightforward, the Suzuki Boulevard S40 has all the makings of a sensible beginner’s bike — a stigma that would normally narrow its appeal to only the newest of riders.

But to Casey Stevenson and Ryan Rajewski the S40 is an ideal starting point for something far more ambitious. They see the single-cylinder S40 as a blank canvas, the foundation for a runabout with a retro-cool appeal that can draw young urban riders.

Their company, Ryca Motors of Whittier, Calif., has intervened on behalf of the cruiser-style S40, producing a parts kit that rescues the bike from its usual role as a none-too-attractive Harley-Davidson Sportster replica and gives it the identity of a classic cafe racer.

When the transformation is complete, the bike’s spare lines echo those of single-cylinder machines from the likes of BSA and Norton, popular in the 1960s among enthusiasts who stripped them to the basics and raced one another over country lanes between British roadhouses. That cafe-racer style — signified by low-mounted handlebars, footpegs repositioned to the rear and barely muffled exhaust pipes — eventually grew into a trend.

The cafe racer is enjoying a resurgence today, to the point of being seen as downright hip. But this time it’s image-conscious young Americans stripping inexpensive Japanese bikes.

Ryca’s CS-1 is a thoughtfully engineered kit that includes custom bodywork, suspension parts and controls of its own design. The Suzuki that serves as its basis has been manufactured nearly unchanged since the ’80s — it still uses a carburetor to feed its air-cooled 652 cc engine.

Mr. Stevenson, the Ryca’s designer, is an ex-NASA engineer who saw potential in the S40’s unprepossessing chassis. He reshaped and downsized the fuel tank, and created a sleek seat, tail section and side panels. Longer shock absorbers at the rear and a shortened front fork leveled the machine’s stance, and rear-set footpegs and clip-on handlebars completed the makeover.

That prototype looked and worked so well that Mr. Stevenson and Mr. Rajewski decided to offer a conversion kit. In the two years since, more than 300 kits have been sold, Mr. Rajewski said.

The basic package sells for $2,495, not including shipping or, for that matter, a donor bike, which costs anywhere from $800 for a neglected 1986 model, then known as a Savage, to $5,699, including shipping, for a 2012 S40 from a dealer.

Assembly is required. Buyers send the factory fuel tank and rear-wheel hub to Ryca, where the tank is reshaped, reducing its capacity to about 2.2 gallons from the original 2.8, and the wheel is relaced to fit an 18-inch rim.

Ryca details the entire process in a series of YouTube videos. But for riders who’d rather not get their hands dirty, Ryca will build an all-new CS-1, using a showroom-fresh S40, for about $9,500, depending on options. Ryca is also encouraging bike shops to buy kits and do conversions locally.

On the street, the Ryca turns heads in a way that mass-produced machines do not. It’s striking and original, with its own aura of a classic thumper mixed with new-millenium chic. I was inspired to drag out my black racing leathers to stay in character: my usual brilliant yellow riding jacket was not going to cut it with the too-cool motorcycle subculture here in Los Angeles.

The Ryca feels tight and tiny, a natural for in-city commuting and short-haul cafe hopping. The riding position is tolerable and the low seat height is perfect for smaller, lighter riders.

The Suzuki engine is smooth, torquey and responsive, its exhaust crackling on downshifts like a Norton Manx slowing for the Creg-ny-baa section of the famed Isle of Man racecourse.

Brakes and suspension are not quite up to racing standards. The Ryca kit’s shock absorbers are too flaccid for any but the lightest, slowest riders, and the stock Suzuki fork, its travel reduced two inches by internal spacers, is just as uninspired. The front brake, a small single disc, requires a determined pull on the lever.

None of these problems are deal-breakers. The basic frame, engine and riding position are sound. Stiffer springs front and rear, higher-viscosity fork oil and stickier front brake pads would be economical upgrades.

But if the CS-1 is not nearly as fast through a set of switchbacks as it looks, does it at least pass the hipness test? The two giggling teenage girls who chased me up Interstate 405 in their Camry just to snap it on their iPhones voted yes.